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<span style="display: inline-block; border: none; padding: 0cm"><font face="Calibri, serif"><font size="3" style="font-size: 12pt"><span lang="en-US"><strong class="western"><span style="font-variant: normal"><font color="#111111"><font face="Arial, sans-serif"><font size="1" style="font-size: 7pt"><span style="letter-spacing: normal"><span style="font-style: normal"><b><span style="background: #ffffff">SCAN</b></span></font></font></strong></span></font></font><font size="3" style="font-size: 12pt"><strong class="cjk"><font size="1" style="font-size: 7pt"><span style="font-style: normal"><b>调度算法</b></span></font></strong></span></span></font></span><span style="font-variant: normal"><font color="#111111"><span style="letter-spacing: normal"><span style="background: #ffffff"><font size="1" style="font-size: 7pt"><span style="font-style: normal">，也被称为</span></font></span></span></font></span><strong class="cjk"><span style="font-variant: normal"><font color="#111111"><span style="letter-spacing: normal"><span style="background: #ffffff"><font size="1" style="font-size: 7pt"><span style="font-style: normal"><b>电梯算法</b></span></font></span></span></font></span></strong><span style="font-variant: normal"><font color="#111111"><span style="letter-spacing: normal"><span style="background: #ffffff"><font size="1" style="font-size: 7pt"><span style="font-style: normal">，是一种磁盘调度算法，用于优化磁头移动，减少寻道时间，提高磁盘性能。该算法的工作原理类似于电梯运行：磁头从一个方向开始移动，处理沿途的所有请求，直到达到该方向的最后一个请求，然后改变方向并重复该过程。</span></font></span></span></font></span></font></span></p>
<p align="left" style="margin-bottom: 0.21cm; line-height: 0.39cm; widows: 2; border: none; padding: 0cm; orphans: 2; page-break-inside: auto; page-break-after: auto">
<span style="display: inline-block; border: none; padding: 0cm"><font size="3" style="font-size: 12pt"><span style="font-variant: normal"><font color="#111111"><span style="letter-spacing: normal"><span style="background: #ffffff"><font size="1" style="font-size: 8pt"><span style="font-style: normal"><b>算法原理</b></span></font></span></span></font></span></font></span></p>
<p align="left" style="margin-bottom: 0.14cm; line-height: 0.39cm; border: none; padding: 0cm; orphans: 2; widows: 2; page-break-inside: auto; page-break-after: auto">
<span style="display: inline-block; border: none; padding: 0cm"><font size="3" style="font-size: 12pt"><span style="font-variant: normal"><font color="#111111"><span style="letter-spacing: normal"><span style="background: #ffffff"><font size="1" style="font-size: 7pt"><span style="font-style: normal">在</span></font></span></span></font></span></font><font face="Calibri, serif"><font size="3" style="font-size: 12pt"><span lang="en-US"><strong class="western"><span style="font-variant: normal"><font color="#111111"><font face="Arial, sans-serif"><font size="1" style="font-size: 7pt"><span style="letter-spacing: normal"><span style="font-style: normal"><b><span style="background: #ffffff">SCAN</b></span></font></font></strong></span></font></font><font size="3" style="font-size: 12pt"><strong class="cjk"><font size="1" style="font-size: 7pt"><span style="font-style: normal"><b>算法</b></span></font></strong></span></span></font></span><span style="font-variant: normal"><font color="#111111"><span style="letter-spacing: normal"><span style="background: #ffffff"><font size="1" style="font-size: 7pt"><span style="font-style: normal">中，磁头从磁盘的一端开始，向另一端移动，并在移动过程中处理所有遇到的请求。当磁头到达磁盘的一端时，它会改变移动方向，就像电梯到达楼层的顶部或底部后改变方向一样。这种方法确保了所有请求都会被处理，同时也尽量减少了磁头的移动距离。</span></font></span></span></font></span></font></span></p>
<p align="left" style="margin-bottom: 0.21cm; line-height: 0.39cm; widows: 2; border: none; padding: 0cm; orphans: 2; page-break-inside: auto; page-break-after: auto">
<span style="display: inline-block; border: none; padding: 0cm"><font size="3" style="font-size: 12pt"><span style="font-variant: normal"><font color="#111111"><span style="letter-spacing: normal"><span style="background: #ffffff"><font size="1" style="font-size: 8pt"><span style="font-style: normal"><b>算法优势</b></span></font></span></span></font></span></font></span></p>
<p align="left" style="margin-bottom: 0.14cm; line-height: 0.39cm; border: none; padding: 0cm; orphans: 2; widows: 2; page-break-inside: auto; page-break-after: auto">
<span style="display: inline-block; border: none; padding: 0cm"><font face="Calibri, serif"><font size="3" style="font-size: 12pt"><span lang="en-US"><strong class="western"><span style="font-variant: normal"><font color="#111111"><font face="Arial, sans-serif"><font size="1" style="font-size: 7pt"><span style="letter-spacing: normal"><span style="font-style: normal"><b><span style="background: #ffffff">SCAN</b></span></font></font></strong></span></font></font><font size="3" style="font-size: 12pt"><strong class="cjk"><font size="1" style="font-size: 7pt"><span style="font-style: normal"><b>算法</b></span></font></strong></span></span></font></span><span style="font-variant: normal"><font color="#111111"><span style="letter-spacing: normal"><span style="background: #ffffff"><font size="1" style="font-size: 7pt"><span style="font-style: normal">的优势在于它提供了一种公平的调度方式，所有请求都会被服务，没有被忽略的风险。此外，它减少了磁头移动的距离，相比于</span></font></span></span></font></span></font><font face="Calibri, serif"><font size="3" style="font-size: 12pt"><span lang="en-US"><span style="font-variant: normal"><font color="#111111"><font face="Arial, sans-serif"><font size="1" style="font-size: 7pt"><span style="letter-spacing: normal"><span style="font-style: normal"><span style="background: #ffffff">**</span></font></font></span></font></font><font size="3" style="font-size: 12pt"><font size="1" style="font-size: 7pt"><span style="font-style: normal">先来先服务（</span></font></font><font face="Calibri, serif"><font size="3" style="font-size: 12pt"><span lang="en-US"><font face="Arial, sans-serif"><font size="1" style="font-size: 7pt"><span style="font-style: normal">FCFS</span></font></font></span></font></font><font size="3" style="font-size: 12pt"><font size="1" style="font-size: 7pt"><span style="font-style: normal">）</span></font></span></span></font></span><strong class="cjk"><span style="font-variant: normal"><font color="#111111"><span style="letter-spacing: normal"><span style="background: #ffffff"><font size="1" style="font-size: 7pt"><span style="font-style: normal"><b>和</b></span></font></span></span></font></span></strong><span style="font-variant: normal"><font color="#111111"><span style="letter-spacing: normal"><span style="background: #ffffff"><font size="1" style="font-size: 7pt"><span style="font-style: normal">最短寻道时间优先（</span></font></span></span></font></span></font><font face="Calibri, serif"><font size="3" style="font-size: 12pt"><span lang="en-US"><span style="font-variant: normal"><font color="#111111"><font face="Arial, sans-serif"><font size="1" style="font-size: 7pt"><span style="letter-spacing: normal"><span style="font-style: normal"><span style="background: #ffffff">SSTF</span></font></font></span></font></font><font size="3" style="font-size: 12pt"><font size="1" style="font-size: 7pt"><span style="font-style: normal">）</span></font></font><font face="Calibri, serif"><font size="3" style="font-size: 12pt"><span lang="en-US"><font face="Arial, sans-serif"><font size="1" style="font-size: 7pt"><span style="font-style: normal">**</span></font></font></span></font></font><font size="3" style="font-size: 12pt"><font size="1" style="font-size: 7pt"><span style="font-style: normal">算法，</span></font></font><font face="Calibri, serif"><font size="3" style="font-size: 12pt"><span lang="en-US"><font face="Arial, sans-serif"><font size="1" style="font-size: 7pt"><span style="font-style: normal">SCAN</span></font></font></span></font></font><font size="3" style="font-size: 12pt"><font size="1" style="font-size: 7pt"><span style="font-style: normal">算法在多数情况下能够提供更好的性能。</span></font></font></span></span></font></span></span></p>
<p align="left" style="margin-bottom: 0.21cm; line-height: 0.39cm; widows: 2; border: none; padding: 0cm; orphans: 2; page-break-inside: auto; page-break-after: auto">
<span style="display: inline-block; border: none; padding: 0cm"><font size="3" style="font-size: 12pt"><span style="font-variant: normal"><font color="#111111"><span style="letter-spacing: normal"><span style="background: #ffffff"><font size="1" style="font-size: 8pt"><span style="font-style: normal"><b>算法示例</b></span></font></span></span></font></span></font></span></p>
<p align="left" style="margin-bottom: 0.14cm; line-height: 0.39cm; border: none; padding: 0cm; orphans: 2; widows: 2; page-break-inside: auto; page-break-after: auto">
<span style="display: inline-block; border: none; padding: 0cm"><font size="3" style="font-size: 12pt"><span style="font-variant: normal"><font color="#111111"><span style="letter-spacing: normal"><span style="background: #ffffff"><font size="1" style="font-size: 7pt"><span style="font-style: normal">假设磁头当前位于柱面</span></font></font><font face="Calibri, serif"><font size="3" style="font-size: 12pt"><span lang="en-US"><font face="Arial, sans-serif"><font size="1" style="font-size: 7pt"><span style="font-style: normal">53</span></font></font></span></font></font><font size="3" style="font-size: 12pt"><font size="1" style="font-size: 7pt"><span style="font-style: normal">，并且有一系列请求在柱面</span></font></font><font face="Calibri, serif"><font size="3" style="font-size: 12pt"><span lang="en-US"><font face="Arial, sans-serif"><font size="1" style="font-size: 7pt"><span style="font-style: normal">98,
183, 37, 122, 14, 124, 65,
67</span></font></font></span></font></font><font size="3" style="font-size: 12pt"><font size="1" style="font-size: 7pt"><span style="font-style: normal">等待处理。如果磁头开始向</span></font></font><font face="Calibri, serif"><font size="3" style="font-size: 12pt"><span lang="en-US"><font face="Arial, sans-serif"><font size="1" style="font-size: 7pt"><span style="font-style: normal">0</span></font></font></span></font></font><font size="3" style="font-size: 12pt"><font size="1" style="font-size: 7pt"><span style="font-style: normal">号柱面方向移动，它会先处理</span></font></font><font face="Calibri, serif"><font size="3" style="font-size: 12pt"><span lang="en-US"><font face="Arial, sans-serif"><font size="1" style="font-size: 7pt"><span style="font-style: normal">37</span></font></font></span></font></font><font size="3" style="font-size: 12pt"><font size="1" style="font-size: 7pt"><span style="font-style: normal">和</span></font></font><font face="Calibri, serif"><font size="3" style="font-size: 12pt"><span lang="en-US"><font face="Arial, sans-serif"><font size="1" style="font-size: 7pt"><span style="font-style: normal">14</span></font></font></span></font></font><font size="3" style="font-size: 12pt"><font size="1" style="font-size: 7pt"><span style="font-style: normal">号柱面的请求，然后在</span></font></font><font face="Calibri, serif"><font size="3" style="font-size: 12pt"><span lang="en-US"><font face="Arial, sans-serif"><font size="1" style="font-size: 7pt"><span style="font-style: normal">0</span></font></font></span></font></font><font size="3" style="font-size: 12pt"><font size="1" style="font-size: 7pt"><span style="font-style: normal">号柱面改变方向，接着处理</span></font></font><font face="Calibri, serif"><font size="3" style="font-size: 12pt"><span lang="en-US"><font face="Arial, sans-serif"><font size="1" style="font-size: 7pt"><span style="font-style: normal">65,
67, 98, 122, 124, 183</span></font></font></span></font></font><font size="3" style="font-size: 12pt"><font size="1" style="font-size: 7pt"><span style="font-style: normal">号柱面的请求。这样的调度方式使得磁头移动的总距离相对较小，提高了磁盘的整体性能。</span></font></font></span></span></font></span></span></p>
<p align="left" style="margin-bottom: 0.21cm; line-height: 0.39cm; widows: 2; border: none; padding: 0cm; orphans: 2; page-break-inside: auto; page-break-after: auto">
<span style="display: inline-block; border: none; padding: 0cm"><font size="3" style="font-size: 12pt"><span style="font-variant: normal"><font color="#111111"><span style="letter-spacing: normal"><span style="background: #ffffff"><font size="1" style="font-size: 8pt"><span style="font-style: normal"><b>实际应用</b></span></font></span></span></font></span></font></span></p>
<p align="left" style="margin-bottom: 0.14cm; line-height: 0.39cm; border: none; padding: 0cm; orphans: 2; widows: 2; page-break-inside: auto; page-break-after: auto">
<span style="display: inline-block; border: none; padding: 0cm"><font size="3" style="font-size: 12pt"><span style="font-variant: normal"><font color="#111111"><span style="letter-spacing: normal"><span style="background: #ffffff"><font size="1" style="font-size: 7pt"><span style="font-style: normal">在实际应用中，</span></font></span></span></font></span></font><font face="Calibri, serif"><font size="3" style="font-size: 12pt"><span lang="en-US"><strong class="western"><span style="font-variant: normal"><font color="#111111"><font face="Arial, sans-serif"><font size="1" style="font-size: 7pt"><span style="letter-spacing: normal"><span style="font-style: normal"><b><span style="background: #ffffff">SCAN</b></span></font></font></strong></span></font></font><font size="3" style="font-size: 12pt"><strong class="cjk"><font size="1" style="font-size: 7pt"><span style="font-style: normal"><b>算法</b></span></font></strong></span></span></font></span><span style="font-variant: normal"><font color="#111111"><span style="letter-spacing: normal"><span style="background: #ffffff"><font size="1" style="font-size: 7pt"><span style="font-style: normal">通常不会在磁盘的整个宽度内移动磁臂，而是只移动到一个方向的最远请求为止，这种变体被称为</span></font></span></span></font></span></font><font face="Calibri, serif"><font size="3" style="font-size: 12pt"><span lang="en-US"><strong class="western"><span style="font-variant: normal"><font color="#111111"><font face="Arial, sans-serif"><font size="1" style="font-size: 7pt"><span style="letter-spacing: normal"><span style="font-style: normal"><b><span style="background: #ffffff">LOOK</b></span></font></font></strong></span></font></font><font size="3" style="font-size: 12pt"><strong class="cjk"><font size="1" style="font-size: 7pt"><span style="font-style: normal"><b>调度</b></span></font></strong></span></span></font></span><span style="font-variant: normal"><font color="#111111"><span style="letter-spacing: normal"><span style="background: #ffffff"><font size="1" style="font-size: 7pt"><span style="font-style: normal">。此外，还有</span></font></span></span></font></span></font><font face="Calibri, serif"><font size="3" style="font-size: 12pt"><span lang="en-US"><strong class="western"><span style="font-variant: normal"><font color="#111111"><font face="Arial, sans-serif"><font size="1" style="font-size: 7pt"><span style="letter-spacing: normal"><span style="font-style: normal"><b><span style="background: #ffffff">C-SCAN</span></b></span></span></font></font></font></span></strong></span></font></font><font size="3" style="font-size: 12pt"><span style="font-variant: normal"><font color="#111111"><span style="letter-spacing: normal"><span style="background: #ffffff"><font size="1" style="font-size: 7pt"><span style="font-style: normal">和</span></font></span></span></font></span></font><font face="Calibri, serif"><font size="3" style="font-size: 12pt"><span lang="en-US"><strong class="western"><span style="font-variant: normal"><font color="#111111"><font face="Arial, sans-serif"><font size="1" style="font-size: 7pt"><span style="letter-spacing: normal"><span style="font-style: normal"><b><span style="background: #ffffff">C-LOOK</span></b></span></span></font></font></font></span></strong></span></font></font><font size="3" style="font-size: 12pt"><span style="font-variant: normal"><font color="#111111"><span style="letter-spacing: normal"><span style="background: #ffffff"><font size="1" style="font-size: 7pt"><span style="font-style: normal">等变体算法，它们在某些特定情况下可能提供更优的性能。</span></font></span></span></font></span></font></span></p>
<p align="left" style="margin-bottom: 0.14cm; line-height: 0.39cm; border: none; padding: 0cm; orphans: 2; widows: 2; page-break-inside: auto; page-break-after: auto">
<span style="display: inline-block; border: none; padding: 0cm"><font face="Calibri, serif"><font size="3" style="font-size: 12pt"><span lang="en-US"><strong class="western"><span style="font-variant: normal"><font color="#111111"><font face="Arial, sans-serif"><font size="1" style="font-size: 7pt"><span style="letter-spacing: normal"><span style="font-style: normal"><b><span style="background: #ffffff">SCAN</b></span></font></font></strong></span></font></font><font size="3" style="font-size: 12pt"><strong class="cjk"><font size="1" style="font-size: 7pt"><span style="font-style: normal"><b>调度算法</b></span></font></strong></span></span></font></span><span style="font-variant: normal"><font color="#111111"><span style="letter-spacing: normal"><span style="background: #ffffff"><font size="1" style="font-size: 7pt"><span style="font-style: normal">是操作系统中磁盘调度的重要组成部分，它通过优化磁头的移动路径，减少寻道时间，从而提高了磁盘的响应速度和整体性能。在设计磁盘调度策略时，理解和应用</span></font></span></span></font></span></font><font face="Calibri, serif"><font size="3" style="font-size: 12pt"><span lang="en-US"><span style="font-variant: normal"><font color="#111111"><font face="Arial, sans-serif"><font size="1" style="font-size: 7pt"><span style="letter-spacing: normal"><span style="font-style: normal"><span style="background: #ffffff">SCAN</span></font></font></span></font></font><font size="3" style="font-size: 12pt"><font size="1" style="font-size: 7pt"><span style="font-style: normal">算法及其变体可以显著提升系统的</span></font></font><font face="Calibri, serif"><font size="3" style="font-size: 12pt"><span lang="en-US"><font face="Arial, sans-serif"><font size="1" style="font-size: 7pt"><span style="font-style: normal">I/O</span></font></font></span></font></font><font size="3" style="font-size: 12pt"><font size="1" style="font-size: 7pt"><span style="font-style: normal">效率。</span></font></font></span></span></font></span></span></p>
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